Remove completely broken handling of member function pointers

Member function pointers can't possibly be represented as function pointers,
they have a strictly bigger size and attempting to do it resulted in code
which, with a lot of bad casts, compiled, but crashed during run-time.

The proper solution is to represent C++ method pointers with an appropriate
opaque type, but for now this remains broken -- just make it explicitly broken
instead of pretending that it works when it actually has no chance to.

Let "namespace_spaces" unit test pass, as it's not really related to the
function pointers, by adding an explicit SWIGC test to it.

Examples/test-suite/namespace_spaces.i

@@ -16,7 +16,9 @@ public:
     int blah(int x); 
     int spam(int x); 
     Integer bar(Integer x); 
+#ifndef SWIGC
     void (Foo:: *func_ptr) (int);
+#endif
 }; 
  
 inline Foo :: Foo () {}